Well your core clock is only running at 405 mhz which is probably why, I suggest you overclock it to get better performance. If you have no idea how to overclock research and make sure you know what your doing before doing it. Main thing with OC'ing is to watch temps. My 660m I run at 1200mhz core and 3000mhz mem for gaming/benchmark but every GPU is a tad different.
tl;dr: your core clock is only 405 mhz which is probably why
EDIT: I ran it and got a lower score with my GPU OC'ed higher than before
Higher OC:
http://www.3dmark.com/3dmv/4379190Lower OC:
http://www.3dmark.com/3dmv/4426273Wonder why that is....
EDIT EDIT: I reset to Default settings in Nvidia Contl Panel and blasted that Higher score away!
http://www.3dmark.com/3dmv/442629316gb ram 1600mhz
Processor Clock Probably 3.2ghz
Computer: Asus G75VW-BHI7N07
Screen: 17.3" 1920x1080p Anti-Glare Matte
CPU: Intel Core i7 3rd Gen 3630qm 2.4ghz
GPU: Nvidia GTX660m (Max OC without custom Bios)
Memory: 16gb 1600mhz Crucial
HDD:1TB 5400rpm
OS: Win 8 64 bit
Mouse: Razer Naga
Mouse Pad: Rocketfish Gaming Mouse Pad
Headset: Turtle Beach DPX21
Best score on Mark 3D Vantage:
http://www.3dmark.com/3dmv/4426293 14144 3D Marks